The present invention relates to a device and arrangement for limiting and delineating the entrance zone for shock waves launched for therapeutic purposes into the body of a living being such as a human patient.
The DORNIER SYSTEM GMBH (assignee) developed a device for contactless comminution of concrement in the body of a living being, such as a human patient, by means of ultrasonic shock waves. The known device is usually comprised of a tub having in its bottom coupled thereto an ellipsoidal reflector which has two focal points. In one of the focal points a spark discharge produces a shock wave, and the reflector focuses the shock waves fronts into the second focal point. The body of the patient is positioned in the tub such that the concrement, for example a kidney stone, is situated in that second focal point. The shock wavefronts as they converge upon this second focal point penetrate into the concrement and cause spalling and comminution to break up the stone into small parts, even grit, which can be discharged from the body by a natural process. German printed patent application No. 3,146,626 (see U.S. Pat. No. 4,539,989) discloses such a device whereby however the tub is replaced by a liquid filled cushion for purposes of acoustically coupling the shock waves from the generating and focusing device into the body.
Upon transmitting shock waves through body tissue the danger arises that certain organs which are sensitive to shock waves such as the lung, the intestinal tract or bones are exposed to shock wavefronts because the comminution process though having an attenuating effect on the focus shock waves nevertheless does not obliterate these shock waves so that following the concentration of shock waves in the second focal point they continue to propagate into further parts of the body. Also, the initial shock wave must be expected to have fringe portions that never reach the second focal point, or the overall construction of the focussing chamber is such that sensitive organs just happen to be in the path of the shock waves regular.
It has to be noted here that the position of various organs in relation to the body surface varies considerably from patient to patient and is in addition dependent upon the position of the patient particularly with respect to the equipment. Moreover, that position may change when the patient moves. The stones and concrements to be comminuted have most certainly not similar position for all various patients. Therefore it seems inevitable that in some cases, depending upon the locating procedure for the concrement prior to the comminution process it happens that sensitive organs are in fact exposed to the shock wave field. This of course is particularly the case if the target is near the lung or the intestinal tract; if the method is used for the decalcificatioon of mitral flap in the heart or for comminuting gall stones shock waves must be expected to reach these sensitive organs.
Another difference to be observed is that simply for reasons of size, the anatomy of children differs from adults therefore special adaptation is needed for the shock wave field to be applied to a child. For this it has been suggested (see Patent Application No. P33 20 998, corresponding to U.S. Pat. No. 4,622,969) to provide diaphragm rings onto the reflector body. This is a viable and practical solution but cannot be deemed to treat the problem exhaustively for reasons of the high degree of complexity in anatomic structure which varies from patient to patient.